Demystifying climate

Entering the murky world of climate change science can be a daunting prospect, especially with terms such as “projections” and “RCPs” commonly used in technical papers and media posts alike. In this blog, we break down the technical barriers by briefly explaining what these terms really mean and how they relate to the warming we’re likely to experience over the coming century.

How can climate scientists project the future?

Climate change science is complex; because of the number of different factors that influence our climate there is no one single view on what our future climate may be. Scientists have developed three-dimensional representations of the Earth’s climate system, known as Global Climate Models (GCMs), to simulate processes driving our current and future climate (GFDL, 2018). The output of these models are known as climate projections.

GCMs are based on the laws and equations of physics that underpin scientists’ understanding of our climate. However, some of these are so complex there is no (known) single, specific solution to them, so the models try to solve them “numerically”, which means they are approximated. Another factor to consider is that changes can be made to different features in a climate model, such as warming or cooling land surface temperatures. These parameterisations help us to better understand the impact on the climate, whilst adding to the number of projections.

What are climate scenarios?

A standard set of climate change scenarios, developed by leading scientific institutions and released in the IPCC AR5, are used to ensure consistency across GCMs. The scenarios describe a range of possible future conditions based on complex socioeconomic forces driving greenhouse gas and aerosol emissions, e.g. land-use, economic evolution and growth in human population, These scenarios are applied to GCMs to give us climate change projections.

In 2014, a set of scenarios titled Representative Concentration Pathways (RCPs) were introduced. RCPs correspond to different projections of atmospheric greenhouse gas concentrations, the key driver of rising temperatures, and are categorised into four scenarios: RCP2.6, RCP4.5, RCP6.0 and RCP8.5 (van Vuuren et al., 2011). The number for each scenario relates to the total radiative forcing projected by 2100, i.e. the additional energy (heat) in the atmosphere due to greenhouse gases.

The RCPs cover a range of future possibilities. RCP2.6 is a mitigation scenario leading to very low future greenhouse gas concentrations. Essentially, it assumes global greenhouse gas emissions will reduce substantially over time by taking into consideration actions such as widespread use of renewable energy and implementation of sustainable carbon neutral policies.
RCPs4.5 and 6.0 are medium scenarios, in which total radiative forcing stabilises after 2100 due to the application of strategies for reducing greenhouse gas emissions.

Finally, RCP8.5 is the worst-case scenario, characterised by increasing greenhouse gas emissions and therefore a failure to curb warming by 2100.

The link to a warming world

In 2015, a landmark agreement was reached by the United Nations Framework Convention on Climate Change (UNFCC) to combat climate change and accelerate the actions and investments needed for a more sustainable future. The Paris Agreement has since been signed by 184 nations, who have all agreed one of the key aspects – to limit global temperature increase to below 2°C by 2100.

Each RCP can be associated with a temperature change by the end of the century. The Paris Agreement target of 2°C is most closely related to the two medium scenarios, RCP4.5 and RCP6.0 (Figure 1).

Figure 1: Projected global mean surface temperature change for the four Representative Concentration Pathways (RCPs). Intersecting the x-axis at 2100 shows the most likely RCP to help limit warming to 2°C is between RCP4.5 and RCP6.0. Source: IPCC, 2014.

To better understand how the different RCPs may impact global temperature, the leading international body for the assessment on climate change, the Intergovernmental Panel on Climate Change (IPCC), has produced maps showcasing the projected changes (Figure 2).

Figure 2: Change in average surface temperature for 2081 – 2100 relative to 1986 – 2005 under RCP2.6 (left) and RCP8.5 (right) scenarios. Source: IPCC, 2014.

The maps highlight the drastic difference between the two ends of the scenario spectrum and explain why so many nations and industries are now, understandably, becoming increasingly aware of climate change impacts and mitigation strategies.

Combining climate change and catastrophe modelling

One of the key challenges facing the re/insurance industry is how to integrate climate change risk into services to enable forward-planning such as portfolio diversification. There are a variety of existing tools that provide a view of present-day flood risk, such as hazard maps and catastrophe models, so can these be adjusted to offer an insight into potential future changes to flood risk?

JBA has developed a climate change flood catastrophe model, the first of its kind in the UK, to try and answer this very question. The model utilises some of the latest climate change data available to enable users to identify areas more/less susceptible to flood and provide an estimate of loss results by 2040, under a realistic warming scenario.

The world of climate change science can be a difficult one to understand and, with so much uncertainty around our future climate, a challenging one to integrate into re/insurance practice. However, at JBA, we believe it’s important for re/insurers to start thinking about the potential future impact of climate change on their exposure.

Get in touch to find out more about our climate change work, including our UK Climate Change Flood Model.


Geophysical Fluid Dynamics Laboratory. 2018. Climate Modeling. [Online]. [Accessed: 7 December 2018]. Available from:

IPCC. 2014. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.H.Pachauri and L.A.Meyer (eds.)]. Geneva, Switzerland: IPCC.

Van Vuuren, D.P., Edmonds, J., Kainuma, M., Riahi, K., Thomson, A., Hibbard, K., Hurtt, G.C., Kram, T., Krey, V., Lamarque, J., Masui, T., Meinshausen, M. and Nakicenovic, N. 2011. The representative concentration pathways: an overview. Climatic Change. 109 (5), pp.5-31.